Skowron 1966b.

Study characteristics
Methods	Randomised, double‐blind controlled trial
Participants	Study period: December 1964 to March 1965 Setting: tracheitis ward of The Hospital for Sick Children, Toronto, Canada Inclusion criteria: children hospitalised with croup Exclusion criteria: not reported Baseline demographics (N = 200 in total, N = 100 for 1.5 mL dexamethasone compared to placebo): proportion males: 77% mean age in years: 2.3 croup score: not measured
Interventions	1.5 mL (6 mg) dexamethasone compared to placebo (see Skowron 1966a for 1.0 mL dexamethasone compared to placebo) All children were placed in a croupette with moist air, given twice‐daily intramuscular crystalline sodium penicillin (825,000 IU/day) and streptomycin sulphate (0.5 g), as well as secobarbital, 3/4 grain per rectum on admission for children over 6 months. Treatment (N = 56): 1.5 mL (6 mg, based on approximately 0.5 mg/kg) subcutaneous dexamethasone every 6 hours for a total of 4 doses Control (N = 44): 1.5 mL placebo every 6 hours for a total of 4 doses
Outcomes	Readmissions to the hospital; length of stay in the hospital; tracheotomy
Notes	Funding source: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Comment: insufficient information provided to permit a judgement
Allocation concealment (selection bias)	Unclear risk	Quote: "The test material was provided in labelled vials, the content of which was unknown to the investigators. As each child was admitted to the series, he received subcutaneously either material A or material B, according to a random selection code" Comment: bottles were not sequentially numbered, but instead labelled A or B. Unclear where the random selection code was held
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "The test material was provided in labelled vials, the content of which was unknown to the investigators." "After the results were documented, the code was broken"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "The test material was provided in labelled vials, the content of which was unknown to the investigators." "After the results were documented, the code was broken"
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: 3% (N = 6) lost due to protocol deviations
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol identified. All prespecified outcomes in the methods appeared in the results.
Other bias	Unclear risk	Comment: no baseline data presented, impossible to judge if baseline imbalances existed
Overall risk of bias All outcomes	Unclear risk	Comment: at least 1 domain judged as unclear risk, and no domains judged as high risk